This invention relates to electrically isolated high speed optical switching circuits, and more particularly to an optoisolator circuit for an over-voltage protection module in a computer system.
During computer operation certain adverse conditions may occur. In one instance, referred to as a so-called crowbar event, an over-voltage situation is in progress. During a crowbar event, the power system output voltage is in the process of increasing to an unacceptable level.
The response to such an over-voltage is to power down the voltage bus. Time is of the essence in powering down the voltage to avoid placing excessively high voltages on critical semiconductor components beyond design rating. The critical point in such power down situations requires that the power-down occurs before the over voltage reaches a dangerous level. The time frame is measured in tens of microseconds.
Circuitry must be provided to sense this over-voltage condition and instantly produce a shut down condition. What typically happens is that during an over-voltage condition the power system output voltage starts ramping up to a high and unacceptable voltage. Over-voltage sensing circuitry then responds to this ramped up increase in voltage and after processing through some logic, this sensed condition or signal is transmitted through an optical coupler circuit to another module which shuts down the power supply, thereby stopping the over-voltage condition.
Over-voltage situations readily occur during component failure or feedback loop malfunctions or malfunction of bus structures and subsystems. In one typical computer configuration, in connection with the bus structure, there may be five converters set up in parallel with one feedback loop through a regulator intelligence card. In this configuration, the feedback loop is connected through a small twisted pair of cable. Failure of this small twisted pair cable can readily result in an over-voltage condition, where the converters lose their feedback loop, whereupon the converters run open loop, resulting in ever increasing voltages which can result in component failure. Such cable failure can result from actual breakage or even solder joint disconnection or physical jarring loose of the connection.
This over-voltage sensing circuitry will normally be included as part of the power supply module or power system. In such circuitry, as part of the over-voltage sensing, an optoisolator is employed. However, with a single optical coupler, or optoisolator, a significant, unacceptable delay occurs, in the order of fifty microseconds. With a design goal of maintaining the bus voltage at or below a seven volt level at all times, such a delay, under certain conditions, could cause the voltage to approach eight volts in a time span which is substantially less than fifty microseconds, which proves to be unacceptable. Much of this delay has been attributable to time delays inherent in the optoisolator device.
Other devices which could be utilized in place of the optoisolator include pulse transformers, which tend to be exceptionally expensive and require a lot of support circuitry.
In accordance with an aspect of the invention a new and improved instantaneously operating optoisolator switching circuit is provided.